The present invention relates to an inspection system in an automated production line. More particularly, the invention relates to a system and method of inspection of ophthalmic lens that are illuminated with ultraviolet light. The lenses are inspected in containers prior to the sealing process.
Ophthalmic lenses are packaged in small containers commonly called as blister packs. The containers typically contain a single ophthalmic lens submerged in saline solution. Prior art systems disclose inspection systems using LED illumination in the form of back light and front light. These type of inspection systems suffer from certain limitations in detecting very fine cracks, bubbles and edge defects in the lenses due to contaminated saline solution and bubbles in the solution that affects the quality of inspection and increases the inspection time significantly as the software has to perform more analysis of the image to differentiate between real and false defects. Furthermore, typical LED illumination systems have difficulty in highlighting deformities in the lens material, especially if the deformities are orientated along the axis of the illumination. Elaborate methods such as varying the illumination angle, changing the wavelength of the illumination combined with multiple images capturing have to be adopted to enable detailed analysis of different images to detect very fine defects. In spite of these additional painstaking steps to detect fine defects, there are instances, the inspection detects many good lenses as rejects which increases losses to the manufacturer. There are also instances wherein the inspection system accepts defective lenses as good, in which case the customer will encounter faulty lens.
It is a known phenomenon that certain fluorescent materials are capable of absorbing radiated electromagnetic energy in the near ultraviolet spectrum and emitting it at a longer wavelength in the visible spectrum of light. This phenomenon enables various inspection of objects comprising of fluorescent dyes or pigments, illuminated by an ultraviolet radiation source that will re-radiate with luminescence in the visible spectrum.
It is a well-known fact that fluorescent pigments or compounds are used during the manufacturing of contact lens. Typically fluorescent compounds were utilized so laboratories could identify and detect materials and prevent duplication and identify counterfeits of the base material used in the manufacture of Contact lens. Counterfeiting and substitution of lens materials and misleading advertising had become a common place. Fluorescence is a process of photo-luminescence by which light of short wavelengths, either in the ultraviolet or the visible regions of the electromagnetic spectrum, is absorbed and re-radiated at longer wavelengths. The re-emission occurs within the visible region of the light spectrum. The fluorescent compounds in the contact lens material exhibit the phenomenon of fluorescing under ultraviolet light. The fluorescent light emanating from the pigment in the contact lens material, is reflected within the polished optical surfaces of the lens and concentrated at the lens edge or any edge formed as a result of a defect or other deformity. The phenomena of fluorescing is especially pronounced at the edges of the material and where the material is broken or disrupted in its physical characteristics. No fluorescence is visible when the material is illuminated with standard LED illumination or Infra Red illumination. However the fluorescence is obvious when the same material is illuminated using ultraviolet illumination. Accordingly, defects such as voids, bubbles or cuts within the material will appear as bright (pixels) on the digital image captured by the camera, since little or no light in the fluorescent wavelength will be emitted from the section of the material representative of the defects. Accordingly, the present invention is particularly suited for detecting defects in pigmented lens material, even where those voids may be undetectable to the naked eye.
An apparatus and methods are needed that can produce consistently enhanced images of contact lenses suspended in saline solution, to enable reliable and robust detection of edge defects, breakages and bubbles in the lenses. This is the objective of the present invention.